The Ethernet (registered trade mark) technique developed as a LAN (Local Area Network) technology has been more and more important in a WAN (Wide Area Network). Many Ethernet traffics are transferred via WAN.
When an Ethernet signal is transmitted via an electric/optical cable, a bit sequence provided by an upper layer is coded instead of being transmitted without change in order to facilitate transmission. For example, 10G Ethernet uses a 64B/66B block code (see, for example, Non-Patent Document 1). The 64B/66B block code is a 66-bit binary digital signal containing a 64-bit binary digital signal and a 2-bit synchronous header. The 64B/66B block code is excellent in detection of bit errors. The 64B/66B block code involves data blocks containing only data and control blocks containing control codes. A combination of data blocks and control blocks allows Ethernet signals, which have a variable Ethernet frame length, to be efficiently transmitted. Furthermore, the 64B/66B block code is appropriately compatible with a serial common interface XAUI (10 Gigabit Attachment Unit Interface) and a parallel common interface XGMII (10 Gigabit Media Independent Interface).
Moreover, the 64B/66B block code is likely to be used in 40G Ethernet and 100G Ethernet, which have been standardized as a next-generation high-speed Ethernet (see Non-Patent Document 8). Furthermore, an optical interface in 40G Ethernet and 100G Ethernet is likely to use parallel transmission in which a plurality of optical signals are transmitted and received in parallel. In particular, MLD (Multi-Lane Distribution) is highly expected to be adopted (see Non-Patent Document 9). MLD is a scheme that uses a mechanism called virtual lanes and which can deal with the plural physical lanes. In the MLD, skew may occur between virtual lanes depending on the transmission status between apparatuses. Thus, skew adjusting markers are indispensable for correcting the skew.
On the other hand, in WAN, in addition to SDH (Synchronous Digital Hierarchy), OTN (Optical Transport Network) has been standardized and used for services (see Non-Patent Document 2). OTN is a leased circuit network configured to tunnel a bit sequence transferred at a rate defined according to the SDH, on a WDM (Wavelength Division Multiplexing) optical network. Three classes for 2.5 Gb/s, 10 Gb/s, and 40 Gb/s are defined for OTN. OTN has a feature using error-correcting codes to carry out high-quality long-distance, and wide-band transmissions.
When a 10G Ethernet signal is transferred on OTN using, for example, an OPU2 (Optical channel Payload Unit 2) frame, various problems may occur as described below. There is a difference between the bit rate (10.3125 Gb/s) of the 10G Ethernet signal and the payload band (9.99528 Gb/s) of the OPU2 frame. The difference between their bitrates prevents the 10G Ethernet signal from being transmitted directly using the OPU2. Thus, a complicated method, a complicated apparatus, and a complicated system are required to transfer the 10G Ethernet signal on OTN. An example of such a method, an apparatus, and a system is based on GFP-F (Generic Framing Procedure) mapping and Direct mapping (see Non-Patent Documents 2 to 4). The GFP-F mapping is a method of terminating the 10G Ethernet signal at a MAC (Media Access Control) level and then using a GFP frame to capsulate the signal except for an IFG (Inter-Frame Gap) portion and a PR (Preamble) portion. Thus, the GFP-F mapping method sets the effective band equal to or lower than the bitrate of the OPU2 frame payload. Furthermore, the direct mapping is a method of increasing a clock rate to widen the payload bitrate of the OPU2 frame up to 10.3125 Gb/s.
Another method is to carry out code conversion to reduce the bit rate (see Non-Patent Documents 5 and 6 and Patent Documents 1 and 2). This method deletes redundant bits from block codes, collects and groups a plurality of the remaining block payloads, and provides control block payloads with position determination information. The method further adds a header indicating whether or not the group contains a control code, and subjects the group to block coding. The method further utilizes a bit difference (corresponding to bits the number of which is equal to that of the deleted redundant bits (for example, 32 bits: 1 bit/block×32 blocks)) resulting from the grouping of the plurality of block payloads from which the redundant bits have been deleted, as redundant bits for error-correcting codes for the grouped block payloads. This provides the payloads with robustness to burst errors. (see Non-Patent Document 7).    Patent Document 1: U.S. Pat. No. 6,952,405    Patent Document 2: U.S. Pat. No. 7,127,653    Non-Patent Document 1: “IEEE Standards 802.3ae-2002”, IEEE, August, 2002, p. 317, FIG. 49-7    Non-Patent Document 2: “ITU-T Recommendation G.709/Y.1331 Interfaces for the Optical Transport Network (OTN)”, ITU-T, March, 2003    Non-Patent Document 3: “Supplement 43 to ITU-G-series Recommendations Transport of IEEE 10G Base-R in Optical Transport Networks (OTN)”, ITU-T, November, 2006    Non-Patent Document 4: Y. Kisaka et al., “Fully transparent multiplexing and transport of 10 GbE-LANPHY signals in 44.6-Gbit/s-based RZ-DQPSK WDM transmission”, Oth1, OFC2007, 2007    Non-Patent Document 5: Stephen J. Trowbridge, “How can 40 Gb Ethernet be designed to fit exiting ODU3 transport?”, IEEE 802.3 Higher Speed Study Group, Jul. 16, 2007, http://grouper.ieee.org/groups/802/3/hssg/public/july07/tro wbridge—01—0707.pdf    Non-Patent Document 6: Kimio Tanaka, “Digital Communication Technology”, TOKAI UNIVERSITY PRESS, pp. 142, March, 1986    Non-Patent Document 7: “IEEE Standards 802.3ap-2007”, IEEE, March, 2007    Non-Patent Document 8: John Jaeger, “HSSG Tutorial MAC/PHY Architecture”, IEEE 802.3 Higher Speed Study Group Meeting, November, 2007, http://www.ieee802.org/3/hssg/public/nov07/index.htm    Non-Patent Document 9: Mark Gustlin, “100GE and 40GE PCS and MLD proposal”, IEEE P802.3ba 40 Gb/s and 100 GB/s Ethernet Task Force, March 2008, http://www.ieee802.org/3/ba/public/mar08/gustlin—01—0308.pdf